Thanks for posting.
The argfile parameter, unfortunately, doesn't offer anything else than the other switches. We do have an internal 'bug' for the lack of documentation around it, but essentially, the same options can be used in the argfile as you can pass anyway.
So you could have an XML argfile containting, for instance:
Therefore the argfile isn't much more useful.
I think the only way you could automate dynamically supplying the server and db would be to write a cleverer batch file that could take input and pass on the variables to the SQL Doc command.